1. Field of the Invention
This invention relates to recovery of hydrocarbon fluids from subterranean earth formations. More particularly, the invention relates to a process wherein cryogenic liquid such as liquid nitrogen is utilized to increase the permeability of a hydrocarbon fluid-containing formation penetrated by a wellbore.
2. Background Art
Presently, hydrocarbon fluids are produced through wells drilled into subterranean earth formations. Once a well is drilled and completed, it is common to treat the formation in order to stimulate the production of hydrocarbon fluids therefrom. One commonly used stimulation treatment involves hydraulically fracturing the formation. However, conventional hydraulic fracturing processes involve producing the fracturing fluid back through the wellbore, and this sometimes leaves permeability-reducing debris in the formation, and proppant sand often plugs horizontal wells. Gaseous fracturing fluids produce problems because of inability to adequately carry proppants and flow diverters, and foam fracturing fluids often leave flow-reducing residues. Also, sand or similar proppants sometimes produce back, plugging the well and/or damaging surface production equipment.
A technique which has been proposed for stimulating methane production from a coal seam is one which is sometimes referred to as "cavity induced stimulation". In one form of that process, a wellbore is charged with a gas followed by a water slug. The well pressure is then reduced and the injected gas and water produce back and create a cavity by breaking up coal around the borehole face.
Cycling of the gas-water injection and blowdown followed by debris cleanout produces an enlarged wellbore cavity. However, this technique is not effective on many coal seams.
A variation of the cavity induced stimulation process in which liquid carbon dioxide is injected into the coal seam is described in U.S. Pat. No. 5,147,111 to Montgomery.
A method of stimulating water flow from a dry well is described in U.S. Pat. No. 4,534,413 to Jaworowsky. That method involves alternate pressurization and depressurization of a well with liquid or gaseous nitrogen or carbon dioxide to fracture the borehole surface.
U.S. Pat. No. 4,391,327 to DeCarlo describes injection of a foamed fluid into a coal seam to improve gas permeability.
U.S. Pat. No. 4,400,034 to Chew describes use of a drying gas to improve coal permeability.
U.S. Pat. No. 4,544,037 to Terry describes a gas injection procedure for treating wet coal prior to producing gas from the coal.
U.S. Pat. No. 5,085,274 to Puri et al describes a method of recovering methane from a coal bed by injection of a desorbing gas.
While the above-described processes have improved production in many cases, there remains a need for an improved stimulation process which is cheaper, safer and more effective than currently available processes.